Primer



ramed Feb. 1, 1944 UNITED STATES PATENT ,oFiica No Drawing.

Serial No. 372.885

c omits. (Cl. 117-76) This invention relates to an improved primer foradhesive sheets and tapes which have a flex- .so -that thepressure-sensitive adhesive-coating with which one side of the tape hasbeen faced is in contact with the uncoated back of the tape when thetape is rolled upon itself. Accordingly, it is of particular importancethat the adhesive for such tapes be of such a nature, and be so anchoredto the-backing, that it will cellulose.

Primers hitherto known and available are not fully satisfactory asbinders between the adhesives and backing herein referred to because of'insuiiicient anchorage to the backing and/or to the adhesive coating. Itfrequently. happens that other, one having a particular aiiinity'for'rei the adhesive and primer are both stripped or to the fact thatthe primer, although adhering adequately to the adhesive, hasinsuiiicient ad- ,hesion or anchorage t the backing. In other from theback- Instances, the adhesive will strip ing andpriming coat. 7

An important feature of the present invention is the improvementinanchorage betWeen the primer and the backing of regenerated cellulose,and also between the primer and the adhesive coating, while the, otheradvantages and desirable characteristics of the adhesive sheets andtapes or the type referred to herein are retained.

' vulcanized rubber in the the To accomplish this purpose, the presentinvention provides a primer cipal constituents, substantially insolublein each generated cellulose; and the otherfor the adhesive, theseconstituents being dispersible in a common vehicle, and without adverseeii'ect upon Thesetwo constituents are respeceach other.

alcohol, and adispersion of vulor rubber-like material preferused in thespecification and claims is intended to be usedin its generic sense toinclude natural rubber, compounded rubber, late rubber substitutes,synthetic rubbers, and the like,

Polyvinyl alcohol may be prepared in accordance with U. 8. Patent No,-.1,672,156, and is available commercially in various degrees of watersolubility and viscosity, depending principally upon the degree ofpolymerization. out the present invention, it is found more contrationsin order to eflect and retain solubility of polyvinyl alcohol in theaqueous primer until it is applied to the backing.

The vulcanized latex or other dispersion of vulcanized rubber orrubber-like material is preferably introduced directly as such into theaqueous primer solution, but if desired unvulcanized latex may be usedinstead, with the addition of suitable vulcanization accelerators, sothat the final primer "coat after drying will contain vulcanized rubber,or rubber-like material.

The primer may be conveniently prepared in accordance with the followingexample, parts being by Weight: I

, Parts Polyvinyl alcohol, PVA #491 (10% solids) '60 Vulcanized latex,"Vultex #V303 solids) 10 These constituents are stirred together,forming a thick pasty cream. It willbe noted that in this example thereare equal parts by weight of polyvinyl alcohol and latex, on the dry orsolids content basis.

The relative amounts of polyvinyl alcohol and primer may vary within afairly large range.v For good results, however, satisfactory amountshave been found to be between about 30 parts polyvinyl alcohol to '10parts rubber, and parts polyvinyl alcohol to so composed of two prinorother suitable parts rubber parts beingbased on solids content. prisingpoiyvizwl alcohol having an aiiinity ior Lesser amounts or polyvinylalcohol a t is, the hydrophilic cellulos backing in combination adhesionto the backing and lesser amounts or with a rubber derived from anaqueous disperthe adhesion to the coating.

be applied to the regenerated desired marine as rubber decrease Theprimer may cellulose sheet or tape in any. by means of a doctor blade.The applied mm, which should be exceedingly thin, dries rapidly, evenwithout the aid or heat, although it may be convenient in apply heat inorder to hasten the processing.

After the primer has dried, the rubber base, usually rubber and estergum, adhesive is spread in suitable thickness, preferably from asolution in a suitable solvent such as toluene or naphtha. Theapplication may be made by a doctor blade means. The solvent is allowedto dry out, either at room temperature or by the use of heat, and theproducts may then be cut, rolled, or otherwise made up into formsuitable for the trade.

sion, said rubber having an amnity tor the hydrophobic rubber baseadhesive coating.

2. In a pressure sensitive adhesive tape having a hydrophilicregenerated cellulose backing and a hydrophobic rubber base pressuresensitive adhesive coating, an intermediate primer coating of film-likeproportions between said backing andsaid adhesive coating, said primercoating comprising polyvinyl alcohol havin an The action of the primer,as already indicated,

is two-fold, the polyvinyl alcohol has a marked aflinity for theregenerated cellulose, and bonds firmly thereto, while the vulcanizedrubber component adheres strongly to the rubber base gum adhesivecoating. The rubber and polyvinyl alcohol in the primer film are sointimately intermixed and closely bound to each other that there is notendency for them to separate under conditions oi storage or use.

Vulcanized latex, or other dispersion of vulcanized rubber, ispreierableto unvulcanized latex or rubber in the primer, because of its peculiarresistance to any tendency of the adhesive coating to soften the primer.

Fillers, coloring agents, and other materials may be incorporated inmaking the primer, if desired, or even a quantity of the rubber base gumadhesive may be mixed with the primer ingredients'to increase adhesiveand primer. In the latter mixture it is preferable to emulsify theadhesive that is to be mixed with the primer, and this can beconveniently accomplished by stirring the adhesive content into theaqueous solution of the primer.

From the foregoing it will be -apparent that there has been provided aprimer having the desired characteristics of adhering to both theadhesive mass and the backing the aiilnity between the of a pressure-.

ailinity for the hydrophilic cellulose backing in combination with avulcanized rubber derived from an aqueous dispersion, said rubber havingan aiiinity tor the hydrophobic rubber base adhesive coatin 3. In apressure sensitive adhesive tape having a hydrophilic regeneratedcellulose backing and a hydrophobic rubber base pressure sensitiveadhesive coating, an intermediate primer surface coating of film-likeproportions between said backing and said adhesive coating, said primercoating comprising 30'I0% P yvinyl alcohol based on the solids contentcontained and having an afilnity for the hydrophilic cellulose backingand a corresponding 70-'-30% rubber content made from an aqueousdispersion and based on the solids content and having an aiilnity forthe hydrophobic adhesive coating.

4. In a pressure sensitive adhesive tape having a hydrophilicregenerated cellulose backing and a hydrophobic rubber base pressuresensitive adhesive coating, an interposed primer coating of film-likeproportions comprising substantially 60 parts by weight of 10% polyvinylalcohol having an ailinity for the hydrophiliccellulose backing andsubstantially 10 parts by weight of a rubber made from an aqueousdispersion and based on sensitive adhesive tape, that is, of providingan excellent anchorage, without detrimentally afiecting the necessaryand desirable characteristics of a good pressure-sensitive adhesivetape.

It will be obvious to those skilled in the art that minor variations inthe details of composition may be made without departing from the spiritand scope of this invention as defined in the following claims.

I claim:

1. In a pressure sensitive adhesive tape having a hydrophilicregenerated cellulose backing and a hydrophobic rubber base pressuresensitive adhesive coating, an intermediate primer coating or film-likeproportions between said backing-and said adhesive coating, said primercoating comthe'solids content, and having an aillnity for thehydrophobic adhesive coating.

5. In a pressure sensitive adhesive tape havin a hydrophilic regeneratedcellulose backing and a hydrophobic rubber base pressure sensitiveadhesive coating, an intermediate primer surface coating of film-likeproportions comprising a mixture oi equal parts on a dry solids basis ofpolyvinyl alcohol having an aflinity for the hydrophilie cellulosebacking and .a rubber having an aillnity for the hydrophobic adhesivecoating and made from an aqueous dispersion of a rubber.

6. In a. pressure sensitive adhesive tape having a flexible,nonflbro'us, cellulosic, film-like hydrophilic backing, having a smooth,nonporous surface and ,a hydrophobic rubber base pressure a sensitiveadhesive coating, an intermediate primer coating of film-likeproportions between said

